Feedback controlled polishing processes

ABSTRACT

Methods and apparatus for feedback controlled polishing. A computer program product for generating feedback for chemical mechanical polishing. The product includes instructions operable to cause a processor to receive monitoring information during a current polishing cycle in which a first polishing process is performed on a substrate that includes a metal layer. The first polishing process clears the metal layer from the substrate during the current polishing cycle. The product includes instructions to calculate a representation of a clearing profile of the first polishing process. The calculation is based on the monitoring information received during the current polishing cycle. The product includes instructions to detect non-uniformity in the representation. The product includes instructions to generate, from the non-uniformity detected, feedback information for improving the uniformity of a clearing profile of the first polishing process for a subsequent polishing cycle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional and claims the benefit of priorityunder 35 U.S.C. Section 120 of U.S. application Ser. No. 10/396,299,filed Mar. 24, 2003, now U.S. Pat. No. 7,024,268, which claims thebenefit of priority of U.S. Provisional Application Ser. No. 60/366,271,filed on Mar. 22, 2002. The disclosure of each prior application isconsidered part of and is incorporated by reference in the disclosure ofthis application.

BACKGROUND

The present invention relates to chemical mechanical polishing ofsubstrates.

An integrated circuit is typically formed on a substrate by thesequential deposition of conductive, semiconductive, or insulativelayers on a silicon wafer. One fabrication step involves depositing afiller layer over a non-planar surface, and planarizing the filler layeruntil the top surfaces of raised structures of the underlying layer areexposed. For example, a conductive filler layer can be deposited on apatterned insulative layer to fill the trenches or holes in theinsulative layer. In this case, the portion of the layer that is raisedabove the bottom of the trenches or holes form the raised pattern. Thefiller layer is then polished until the raised pattern of the insulativelayer is exposed. The process of planarizing the filler layer until thetop surfaces of raised structures of the underlying layer are exposed isalso referred to as clearing the filler layer. The time required toclear the filler layer will be referred to in this specification as timeclearing time. After planarization, the portions of the conductive layerremaining between the raised pattern of the insulative layer form vias,plugs, and lines that provide conductive paths between thin filmcircuits on the substrate. Copper damascene is one example of the abovedescribed fabrication step.

Chemical mechanical polishing (“CMP”) is one polishing technique thatcan be used for planarization. CMP typically requires that the substratebe mounted on a carrier or polishing head. The exposed surface of thesubstrate is placed against a rotating polishing disk pad or belt pad.The polishing pad can be either a “standard” pad or a fixed-abrasivepad. A standard pad has a durable roughened surface, whereas afixed-abrasive pad has abrasive particles held in a containment media.The carrier head provides a controllable load on the substrate to pushit against the polishing pad. A polishing slurry, including at least onechemically-reactive agent, and abrasive particles if a standard pad isused, is supplied to the surface of the polishing pad.

Planarization can generally include different polishing processes. Forexample, planarization can include a first polishing process, forremoving the bulk of a filler layer, and a second polishing process, forremoving the small amount of the filler layer remaining. The termpolishing process refers to a combination of particular actionsperformed, in a particular sequence, using particular devices andparticular materials to remove material. A polishing process can applyone or more polishing techniques.

A polishing process has parameters, exhibits characteristics, and yieldsresults. Parameters of a polishing technique can include, for example,slurry flow rate, force on a abrasive surface being used to polish thesubstrate, and the radial speed at which the abrasive surface is beingrotated. The characteristics of a polishing process can be the manner inwhich the process removes material, also referred to as the removalprofile of the polishing process. A removal profile of a polishingprocess, which, as described, is a manner in which the polishing processremoves material, is different from a thickness profile of a layer,which is the shape of a cross section of the layer. A removal profile isalso different from a clearing profile of a substrate, which is theresulting shape of a cross section of a substrate after a filler layerhas been cleared. Performing a polishing process on a substrate, thathas an initial or pre-polish thickness profile, usually changes thepre-polish thickness profile to a resulting or post-polish thicknessprofile.

When they are used to manufacture integrated circuits, polishingprocesses are usually performed in cycles. For example, given aparticular polishing process, the actions of this particular process arerepeated for each substrate in an assembly line of substrates. A cyclecan include one or more polishing processes. For example, given thefirst and second polishing processes described above, the actions ofthese processes are repeated for each substrate in the assembly line ofsubstrates.

A clearing profile of a substrate is typically not uniform. Whenplanarization includes a first and a second polishing process, such as,for example, the above described polishing processes, there are threepossible causes of the non-uniformity. These are variations in thepre-polish thickness profile of the substrate and variations in theremoval profiles of the first and second polishing processes being usedto clear a filler layer from the substrate.

A polishing process such as, for example, one that applies CMP, iscomplete when a substrate layer has been planarized to a desiredflatness or thickness, when a filler layer has been cleared, or when adesired amount of material has been removed. The completion or end ofthe polishing process is sometimes referred to as the polishing endpoint. In-situ monitoring of the substrate can been performed, forexample, with optical or capacitance sensors, in order to detect apolishing endpoint. Other proposed endpoint detection techniques haveinvolved measurements of friction, motor current, slurry chemistry,acoustics and conductivity. One detection technique that has beenconsidered is to induce an eddy current in the metal layer and measurethe change in the eddy current as the metal layer is removed.

SUMMARY

The invention provides methods and apparatus, including computer programproducts, for performing feedback-controlled polishing processes.

In general, in one aspect, the invention provides a computer programproduct for generating feedback for chemical mechanical polishing. Theproduct includes instructions operable to cause a processor to receivemonitoring information during a current polishing cycle in which a firstpolishing process is performed on a substrate that includes a metallayer. The first polishing process clears the metal layer from thesubstrate during the current polishing cycle. The product includesinstructions to calculate a representation of a clearing profile of thefirst polishing process. The calculation is based on the monitoringinformation received during the current polishing cycle. The productincludes instructions to detect non-uniformity in the representation.The product includes instructions to generate, from the non-uniformitydetected, feedback information for improving the uniformity of aclearing profile of the first polishing process for a subsequentpolishing cycle. The product is tangibly stored on machine-readablemedium.

In general, in another aspect, the inventions provides a method forgenerating feedback for chemical mechanical polishing. The methodincludes receiving monitoring information during a first polishing cyclein which a first polishing process is performed on a substrate thatincludes a metal layer. The monitoring information includes informationfor two or more sampling regions that correspond to different annularregions of the substrate. The first polishing process clears the firstmetal layer from the substrate during the first polishing cycle. Themethod includes calculating, for each sampling region, a clearing timeof the first polishing process, the calculation being based on themonitoring information received. The method includes determining atarget profile for a subsequent polishing cycle, the calculating beingbased on the clearing times calculated.

Possible advantages of implementations of the invention can include oneor more of the following. Monitoring information, obtained during onepolishing cycle and from one polishing station where a first polishingprocess is performed, can be used to adjust either the first polishingprocess in a subsequent polishing cycle or a second polishing process inthe subsequent cycle. The first and second polishing processes are bothperformed for each polishing cycle. The second polishing process is onethat is performed before the first polishing process is performed. Theclearing times for different regions of a substrate can be derived fromthe monitoring information and, furthermore, can be used to adjust thepolishing processes. The use of clearing times advantageously accountsfor non-uniform removal profiles of the polishing processes, withoutrequiring calculations or measurement of removal rates. Feedback asdescribed in this specification can adjust for the slow drift in thepolishing processes that might result from the aging of consumables suchas, for example, polishing pad, conditioning disk, slurry, retainingrings on a head. The feedback can be controlled by software so thatadjustment of a polishing process is head-specific, which can thusaccount for slight process differences between different polishingheads. Non-uniformity of a clearing profile is convergently reducedafter several cycles.

Other features and advantages of the invention will become apparent fromthe following description, including the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method for feedback controlledpolishing.

FIG. 2 is a schematic exploded perspective view of a chemical mechanicalpolishing apparatus.

FIG. 3A is a schematic side view, partially cross-sectional, of achemical mechanical polishing station that includes an eddy currentmonitoring system and an optical monitoring system.

FIG. 3B is a schematic top view of a platen from the polishing stationof FIG. 3A.

FIG. 3C shows an example eddy current monitoring system.

FIG. 4 is a graph illustrating an amplitude trace from the opticalmonitoring system.

FIG. 5 is a flowchart illustrating a method for feedback-controlledpolishing of a metal layer.

FIG. 6 is a flowchart illustrating an alternative method forfeedback-controlled polishing of a metal layer.

DETAILED DESCRIPTION

A polishing cycle includes a first polishing process and a secondpolishing process that is performed after the first process isperformed. The first polishing process is performed at a first polishingstation. The second polishing process is performed at a second polishingstation. In this implementation of a polishing cycle, monitoringinformation obtained from the second polishing station during a currentpolishing cycle is used as feedback to adjust either the first or secondpolishing process of a subsequent polishing cycle. After several cycles,the adjusted process can clear a filler layer simultaneously everywhereon a substrate.

Monitoring can be done using optical monitors, eddy current monitors, ora combined optical/eddy current monitor. One example of an opticalmonitor is the Full Scan ISRM, available from Applied Materials, ofSanta Clara, Calif. The Full Scan ISRM detects changes in the intensityof light reflected off the substrate work surface. The intensity isnearly constant until the filler layer begins to clear. The Full ScanISRM typically includes a detector that is translated relative to asubstrate being monitored. Usually, the detector is translated so thatdifferent areas of the substrate can be monitored. The Full Scan ISRMprovides a scan, which can be a graph showing reflected intensity as afunction of time or position of the detector. The x-axis of the graphcan be divide into scan regions, each of which can correspond toparticular areas of a substrate being monitored. A particular polishingprocess can have a particular removal profile. In some cases, theremoval profile is not uniform. The described scan regions can bedefined so that the removal rates within each scan region are relativelyconstant.

The Full Scan ISRM can also provide one or more traces. A trace can be agraph showing reflected intensity, as detected by the detector at aparticular position, as a function of time. A trace can, thus, showchange in reflected intensity at a particular area of a substrate beingmonitored.

One example of a combined optical/eddy current monitor is the iScanISRM, also available from Applied Materials. The iScan can provideinformation similar to those described with respect to the Full ScanISRM. Monitoring information, for example, the scan and tracesdescribed, can be sent to a computer for processing and storage. Thecomputer can use the monitoring information as feedback to change thefirst or second polishing processes in subsequent polishing cycles.Devices like the described monitoring systems are further described incommonly assigned U.S. Pat. No. 6,602,724, which is hereby incorporatedby reference in its entirety.

Particular polishing processes can result in different post-polishthickness profiles. The post-polish thickness profile of a substratesubject to the second polishing process or, in cases where the secondpolishing process clears a filler layer, the clearing profile of thesubstrate, for example, can be determined by both the pre-polishthickness profile of the substrate and the removal profile of the secondpolishing process.

As discussed, the interval of time needed to clear a filler layer is theclearing time. The clearing time for each scan region can be derivedfrom the monitoring information and used to adjust the polishingprocesses in the subsequent polishing cycles. Specifically, the clearingtimes can be used to construct either a target pre-polish thicknessprofile of a substrate incoming to the second station or a post-polishthickness profile of the substrate after being subject to the secondpolishing process at the second station. Non-uniformity in the clearingprofile, i.e., the difference between or among clearing times, can bedetected. This information can be used to adjust a polishing cycle. Forexample, if the clearing time for a particular scan region is less thanclearing times of other scan regions, then this information can be usedto increase the clearing time of the particular scan region in the nextpolishing cycle. Adjustment can include making the removal rate slowerby, for example, twenty percent. Adjustment can also include making thepre-polish thickness of the incoming substrate greater by, for example,twenty percent at the area that corresponds to the particular region.

As shown in FIG. 1, a system performing method 100 monitors materialremoval at a second polishing station during a current polishing cycle(step 102). During each polishing cycle, a first and second polishingprocess are sequentially performed on a current substrate. The firstpolishing process is performed at a first polishing station and thesecond polishing process is performed at the second polishing station.The first polishing process can be, for example, a bulk removal processand the second polishing process can be, for example, a slow clearingprocess. Monitoring can be done by, for example, a Full Scan ISRM.

The system uses the monitoring information obtained during the secondpolishing process of the current polishing cycle to calculate clearingtimes of the second polishing process (step 104). The system can use themonitoring information, for example, traces obtained with the Full ScanISRM, which can show intensity of reflected light over time for eachscan region, to calculate the clearing time for each scan region.

The system detects non-uniformity between or among the clearing times(step 106). Detection can be done by comparing the deviation of eachclearing time from an average clearing time. Various other statisticaltechniques can be applied to detect non-uniformity.

The system generates feedback information (step 108). The system can usethe detected non-uniformity to generate feedback information. The systemcan, for example, calculate, for each scan region, a ratio of theaverage clearing time and the clearing time of the region. The ratiocalculated is either less than 1, equal to 1, or greater than 1.Alternatively, the system can generate a target thickness profile, foruse in the next polishing cycle, that is either a post-polish thicknessprofile that the first polishing process produces or a target clearingprofile that the second polishing process produces. The system cancalculate the target profile by calculating the target thickness foreach region. Calculation, in this case, can include taking the abovedescribed ratio and multiplying it to the average of the thicknessprofile as it exists before the current substrate was subject to thesecond polishing process. The post-polish thickness profile can be usedto adjust parameters of the first polishing process. The clearingprofile can be used to adjust parameters of the second polishingprocess.

The system uses the feedback information to adjust, for a subsequentcycle, one of the first polishing process and the second polishingprocess (step 110). When the feedback information is the describedratio, adjustments depends on whether the ratio is less than 1, equal to1, or greater than 1. If, for example, the ratio is greater than 1, thenadjustment can be made to decrease the removal rate at this regionduring the next cycle. Alternatively, the target thickness profile orboth the ratios and the target thickness profile can be similarly usedas feed back information. In the case when the target thickness profileis used, adjustment depends on whether the target thickness for a regionis less than, the same as, or greater than the calculated averagethickness. As cycles occur, the clearing times converges and the typicalnon-uniformity is minimized.

If the removal profile for the second polishing process is available,then a ratio of the average removal rate and the removal rate for eachregion can be calculated and applied to calculate the target thicknessfor each region. The application of such a ration can increase theconvergence rate. That is, the application of this ration of the averageremoval rate and the removal rate for each region can reduce the numberof cycles needed to have the clearing times converge.

How removal rate or a removal profile is changed can be determined by acomputer program product that models the polishing process beingadjusted. The model can be based, for example, on empirical information.A product and model that can be used for feedback as described in thisspecification are further described in commonly assigned U.S. patentapplication Ser. No. 10/393,531, filed on Mar. 21, 2003, the entirespecification is hereby incorporated by reference.

FIG. 2 shows a CMP apparatus 20, in which one or more substrates 10 canbe polished. A description of a similar polishing apparatus 20 can befound in U.S. Pat. No. 5,738,574, the entire disclosure of which isincorporated herein by reference. Polishing apparatus 20 includes aseries of polishing stations 22 a, 22 b and 22 c, and a transfer station23. Transfer station 23 transfers the substrates between the carrierheads and a loading apparatus.

Each polishing station includes a rotatable platen 24 on which is placeda polishing pad 30. The first and second stations 22 a and 22 b caninclude a two-layer polishing pad with a hard durable outer surface or afixed-abrasive pad with embedded abrasive particles. The final polishingstation 22 c can include a relatively soft pad or a two-layer pad. Eachpolishing station can also include a pad conditioner apparatus 28 tomaintain the condition of the polishing pad so that it will effectivelypolish substrates.

As shown in FIG. 3A, a two-layer polishing pad 30 typically has abacking layer 32 which abuts the surface of platen 24 and a coveringlayer 34 which is used to polish substrate 10. Covering layer 34 istypically harder than backing layer 32. However, some pads have only acovering layer and no backing layer. Covering layer 34 can be composedof foamed or cast polyurethane, possibly with fillers, e.g., hollowmicrospheres, and/or a grooved surface. Backing layer 32 can be composedof compressed felt fibers leached with urethane. A two-layer polishingpad, with the covering layer composed of IC-1000 and the backing layercomposed of SUBA-4, is available from Rodel, Inc., of Newark, Del.(IC-1000 and SUBA-4 are product names of Rodel, Inc.).

During a polishing step, a slurry 38 (FIG. 2) containing a liquid (e.g.,deionized water for oxide polishing) and a pH adjuster (e.g., potassiumhydroxide for oxide polishing) can be supplied to the surface ofpolishing pad 30 by a slurry supply port or combined slurry/rinse arm 39(FIG. 2). If polishing pad 30 is a standard pad, slurry 38 can alsoinclude abrasive particles (e.g., silicon dioxide for oxide polishing).

A rotatable multi-head carousel 60 supports four carrier heads 70. (SeeFIG. 2.) The carousel is rotated by a central post 62 about a carouselaxis 64 by a carousel motor assembly (not shown) to orbit the carrierhead systems and the substrates attached thereto between polishingstations 22 and transfer station 23. Three of the carrier head systemsreceive and hold substrates, and polish them by pressing them againstthe polishing pads. Meanwhile, one of the carrier head systems receivesa substrate from and delivers a substrate to transfer station 23.

Each carrier head 70 is connected by a carrier drive shaft 74 to acarrier head rotation motor 76 (shown by the removal of one quarter ofcover 68) so that each carrier head can independently rotate about itown axis. In addition, each carrier head 70 independently laterallyoscillates in a radial slot 72 formed in carousel support plate 66. Adescription of a suitable carrier head 70 can be found in U.S. Pat. Nos.6,422,927 and 6,450,868, the entire disclosures of which areincorporated by reference. In operation, the platen is rotated about itscentral axis 25, and the carrier head is rotated about its central axis71 and translated laterally across the surface of the polishing pad.Devices similar to the carrier head are described in the above mentionedU.S. Pat. No. 6,602,724.

Referring to FIGS. 3A and 3B, a recess 26 is formed in platen 24, and atransparent section 36 is formed in polishing pad 30 overlying recess26. Aperture 26 and transparent section 36 are positioned such that theypass beneath substrate 10 during a portion of the platen's rotation,regardless of the translational position of the carrier head. Assumingthat polishing pad 32 is a two-layer pad, thin pad section 36 can beconstructed by removing a portion of backing layer 32 and inserting atransparent plug 36 into the cover layer 34. The plug 36 can be arelatively pure polymer or polyurethane, e.g., formed without fillers.In general, the material of transparent section 36 should benon-magnetic and non-conductive.

Referring to FIGS. 2, 3A, and 3C, the first polishing station 22 a (FIG.2) includes an in-situ eddy current monitoring system 40 (FIG. 3C) andan optical monitoring system 140 (FIG. 3A). The eddy current monitoringsystem 40 and optical monitoring system 140 can function as a polishingprocess control and endpoint detection system. The second polishingstation 22 b and the final polishing station 22 c can both include justan optical monitoring system, although either may additionally includean eddy current monitoring system.

The optical monitoring system 140, which can function as a reflectometeror interferometer, can be secured to platen 24 in recess 26 adjacent theeddy current monitoring system 40. Thus, the optical monitoring system140 can measure the reflectivity of substantially the same location onthe substrate as is being monitored by the eddy current monitoringsystem 40. Specifically, the optical monitoring system 140 can bepositioned to measure a portion of the substrate at the same radialdistance from the axis of rotation of the platen 24 as the eddy currentmonitoring system 40. Thus, the optical monitoring system 140 can sweepacross the substrate in the same path as the eddy current monitoringsystem 40.

The optical monitoring system 140 includes a light source 144 and adetector 146. The light source generates a light beam 142 whichpropagates through transparent window section 36 and slurry to impingeupon the exposed surface of the substrate 10. For example, the lightsource 144 may be a laser and the light beam 142 may be a collimatedlaser beam. The light laser beam 142 can be projected from the laser 144at an angle a from an axis normal to the surface of the substrate 10. Inaddition, if the hole 26 and the window 36 are elongated, a beamexpander (not illustrated) may be positioned in the path of the lightbeam to expand the light beam along the elongated axis of the window. Ingeneral, the optical monitoring system functions as described in U.S.Pat. Nos. 6,159,07311 and 6,280,289, the entire disclosures of which areincorporated herein by references.

FIG. 4 shows an example of a trace 250 generated by an opticalmonitoring system. The overall shape of intensity trace 250 may beexplained as follows. Initially, the metal layer has some initialtopography because of the topology of the underlying patterned layer.Due to this topography, the light beam scatters when it impinges themetal layer. As the polishing operation progresses in section 252 of thetrace, the metal layer becomes more planar and the reflectivity of thepolished metal layer increases. As the bulk of the metal layer isremoved in section 254 of the trace, the intensity remains relativelystable. Once the oxide layer begins to be exposed in the trace, theoverall signal strength drops quickly in section 256 of the trace. Oncethe oxide layer is entire exposed in the trace, the intensity stabilizesagain in section 258 of the trace, although it may undergo smalloscillations due to interferometric effects as the oxide layer isremoved.

Returning to FIGS. 3A and 3B, the CMP apparatus 20 can also include aposition sensor 80, such as an optical interrupter, to sense when core42 and light source 44 are beneath substrate 10. For example, theoptical interrupter could be mounted at a fixed point opposite carrierhead 70. A flag 82 is attached to the periphery of the platen. The pointof attachment and length of flag 82 is selected so that it interruptsthe optical signal of sensor 80 while transparent section 36 sweepsbeneath substrate 10. Alternately, the CMP apparatus can include anencoder to determine the angular position of platen.

A general purpose programmable digital computer 90 receives theintensity signals and phase shift signals from the eddy current sensingsystem 40, and the intensity signals from the optical monitoring system140. Since the monitoring systems sweep beneath the substrate with eachrotation of the platen, information on the metal layer thickness andexposure of the underlying layer is accumulated in-situ and on acontinuous real-time basis (once per platen rotation). The computer 90can be programmed to sample measurements from the monitoring system whenthe substrate generally overlies the transparent section 36 (asdetermined by the position sensor). As polishing progresses, thereflectivity or thickness of the metal layer changes, and the sampledsignals vary with time. As discussed, the time varying sampled signalsmay be referred to as traces. The measurements from the monitoringsystems can be displayed on an output device 92 during polishing topermit the operator of the device to visually monitor the progress ofthe polishing operation. The computer 90 can use traces to control thepolishing process and determine the end-point of the metal layerpolishing operation. The computer 90 can also process the traces, e.g.,calculate clearing times as described above, and use the informationobtained from processing the traces as feedback to change the polishingprocesses.

In operation, CMP apparatus 20 uses eddy current monitoring system 40and optical monitoring system 140 to determine when the bulk of thefiller layer has been removed and to determine when the underlying stoplayer has been substantially exposed. The computer 90 applies processcontrol and endpoint detection logic to the sampled signals to determinewhen to change process parameter and to detect the polishing endpoint.Possible process control and endpoint criteria for the detector logicinclude local minima or maxima, changes in slope, threshold values inamplitude or slope, or combinations thereof. The CMP apparatus 20 canalso use the monitoring systems, as described above, to provide feedbackcontrol to adjust parameters at each station. Pressure, for example, ofthe described chambers in the carrier head can be adjusted. The rotationspeed of a carrier head, for example, can also be adjusted.

In addition, the computer 90 can be programmed to divide themeasurements from both the eddy current monitoring system 40 and theoptical monitoring system 140 from each sweep beneath the substrate intoa plurality of sampling zones 96, to calculate the radial position ofeach sampling zone, to sort the amplitude measurements into radialranges, to determine minimum, maximum and average measurements for eachsampling zone, and to use multiple radial ranges to determine thepolishing endpoint, as discussed in U.S. Pat. No. 6,399,501, theentirety of which is incorporated herein by reference.

Computer 90 may also be connected to the pressure mechanisms thatcontrol the pressure applied by carrier head 70, to carrier headrotation motor 76 to control the carrier head rotation rate, to theplaten rotation motor (not shown) to control the platen rotation rate,or to slurry distribution system 39 to control the slurry compositionsupplied to the polishing pad. Specifically, after sorting themeasurements into radial ranges, information on the metal film thicknesscan be fed in real-time into a closed-loop controller to periodically orcontinuously modify the polishing pressure profile applied by a carrierhead, as discussed in U.S. Pat. No. 6,776,692, the entirety of which isincorporated herein by reference. For example, the computer coulddetermine that the endpoint criteria have been satisfied for the outerradial ranges but not for the inner radial ranges. This would indicatethat the underlying layer has been exposed in an annular outer area butnot in an inner area of the substrate. In this case, the computer couldreduce the diameter of the area in which pressure is applied so thatpressure is applied only to the inner area of the substrate, therebyreducing dishing and erosion on the outer area of the substrate.

When the computer 90 is programmed to generate feedback as described inFIG. 1, the programming can be implemented as a computer program productthat interacts with programs that controls the CMP apparatus 20. Thecomputer 90 can include a computer program product that takes as inputthe feedback described above in reference to FIG. 1, determines which ofthe described parameters of the CMP apparatus 20 to adjust, and outputscontrol signals for adjusting the CMP apparatus 20. Product similar tothose described are described in the above referenced U.S. patentapplication Ser. No. 10/393,531.

A method of polishing a metal layer, such as a copper layer, is shown inflowchart form in FIG. 5. A current substrate is polished at the firstpolishing station 22 a to remove the bulk of the metal layer (step 502).The polishing process is monitored by the eddy current monitoring system40 (FIG. 3A). When a predetermined thickness, e.g., 2000 Angstroms, ofthe copper layer remains over an underlying barrier layer, the polishingprocess is halted and the current substrate is transferred to the secondpolishing station 22 b (step 504). This first polishing endpoint can betriggered when the phase shift signal exceeds an experimentallydetermined threshold value. Example polishing parameters for the firstpolishing station include a platen rotation rate of 93 rpm, a carrierhead pressure of about 3 psi, and an IC-1010 polishing pad. As polishingprogresses at the first polishing station, the radial thicknessinformation from the eddy current monitoring system 40 can be fed into aclosed-loop feedback system to control the pressure and/or the loadingarea of the carrier head 200 on the substrate. The pressure of theretaining ring on the polishing pad may also be adjusted to adjust thepolishing rate. This permits the carrier head to compensate for thenon-uniformity in the polishing rate or for non-uniformity in thethickness of the metal layer of the incoming substrate. As a result,after polishing at the first polishing station, most of the metal layerhas been removed and the surface of the metal layer remaining on thesubstrate is substantially planarized.

At the second polishing station 22 b, the current substrate is polishedat a lower polishing rate than at the first polishing station. Forexample, the polishing rate is reduced by about a factor of 2 to 4,i.e., by about 50% to 75%. To reduce the polishing rate, the carrierhead pressure can be reduced, the carrier head rotation rate can bereduced, the composition of the slurry can be changed to introduce aslower polishing slurry, and/or the platen rotation rate could bereduced. For example, the pressure on the substrate from the carrierhead may be reduced by about 33% to 50%, and the platen rotation rateand carrier head rotation rate may both be reduced by about 50%. Examplepolishing parameters for the second polishing station 22 b include aplaten rotation rate of 43 rpm, a carrier head pressure of about 2 psi,and an IC-1010 polishing pad.

Optionally, when the polishing begins at the second polishing station,the current substrate may be briefly polished, e.g., for about 10seconds, at a somewhat higher pressure, e.g., 3 psi, and rotation rate,e.g., 93 rpm (step 506). This initial polishing, which can be termed an“initiation” step, may be needed to remove native oxides formed on themetal layer or to compensate for ramp-up of the platen rotation rate andcarrier head pressure so as to maintain the expected throughput.

The polishing process is monitored at the second polishing station 22 bby the optical monitoring system 140 (FIG. 3A). Polishing proceeds atthe second polishing station 22 b until the metal layer is removed andthe underlying barrier layer is exposed (step 508). Of course, smallportions of the metal layer can remain on the substrate, but the metallayer is substantially entirely removed. The optical monitoring systemis useful for determining this endpoint, since it can detect the changein reflectivity as the barrier layer is exposed. Specifically, theendpoint for the second polishing station can be triggered when theamplitude or slope of the optical monitoring signal falls below anexperimentally determined threshold value across all the radial rangesmonitored by the computer. This indicates that the barrier metal layerhas been removed across substantially all of the substrate. Of course,as polishing progresses at the second polishing station 22 b, thereflectivity information from the optical monitoring system 140 can befed into a closed-loop feedback system to control the pressure and/orthe loading area of the carrier head 200 on the substrate to prevent theregions of the barrier layer that are exposed earliest from becomingoverpolished.

The reflectivity information obtained from the optical monitoring system140 can also be used, as described in FIG. 1, to provide feedback, for anext polishing cycle when a next substrate is being polished, to changethe polishing process at either the first polishing station 22 a or thesecond polishing station 22 b (step 510). The reflectivity information,e.g., the described scan and traces, can be used to calculate clearingtimes in each of the sampling zones 96 (FIG. 3B). The computer 90 cancalculate the clearing times of each sampling zone. The sampling zonescan correspond to different annular regions of the current substrate.Calculations include measuring the interval between the time whenpolishing starts and when and end point is reached as determine by, forexample, when the intensity trace for the sampling zone drops (as shown,e.g., in FIG. 4, when the trace drops from intensity level 254 tointensity level 258). Calculations can also include calculating anaverage clearing time and clearing time ratios as described in referenceto FIG. 1.

By reducing the polishing rate before the barrier layer is exposed,dishing and erosion effects can be reduced. In addition, the relativereaction time of the polishing machine is improved, enabling thepolishing machine to halt polishing and transfer to the third polishingstation with less material removed after the final endpoint criterion isdetected. Moreover, more intensity measurements can be collected nearthe expected polishing end time, thereby potentially improving theaccuracy of the polishing endpoint calculation. However, by maintaininga high polishing rate throughout most of the polishing operation at thefirst polishing station, high throughput is achieved. Preferably, atleast 75%, e.g., 80-90%, of the bulk polishing of the metal layer iscompleted before the carrier head pressure is reduced or other polishingparameters are changed.

Once the metal layer has been removed at the second polishing station 22b, the substrate is transferred to the third polishing station 22 c(step 512) for removal of the barrier layer. Example polishingparameters for the second polishing station include a platen rotationrate of 103 rpm, a carrier head pressure of about 3 psi, and an IC-1010polishing pad. Optionally, the substrate may be briefly polished with aninitiation step, e.g., for about 5 seconds, at a somewhat higherpressure, e.g., 3 psi, and platen rotation rate, e.g., 103 rpm (step514). The polishing process is monitored at the third polishing station22 c by an optical monitoring system, and proceeds until the barrierlayer is substantially removed and the underlying dielectric layer issubstantially exposed (step 516). The same slurry solution may be usedat the first and second polishing stations, whereas another slurrysolution may be used at the third polishing station.

An alternative method of polishing a metal layer, such as a copperlayer, is shown in flowchart form in FIG. 6. This method is similar tothe method shown in FIG. 5. However, both the fast polishing step andthe slow polishing step are performed at the first polishing station 22a. Removal of the barrier layer is performed at the second polishingstation 22 b, and a buffing step is performed at the final polishingstation 22 c.

Various aspects of the invention, including the method steps described,can be implemented as a computer program product, i.e., a computerprogram tangibly embodied in an information carrier, e.g., in amachine-readable storage device, for execution by, or to control theoperation of, data processing apparatus, e.g., a programmable processor,a computer, multiple computers, or a test system. A computer program canbe written in any form of programming language, including compiled orinterpreted languages, and it can be deployed in any form, including asa stand-alone program or as a module, component, subroutine, or otherunit suitable for use in a computing environment. A computer program canbe deployed to be executed on one computer or on multiple computers atone site or distributed across multiple sites and interconnected by acommunication network.

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only memory ora random access memory or both. The essential elements of a computer area processor for executing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto-optical disks, or optical disks.

Information carriers suitable for embodying computer programinstructions and data include all forms of non-volatile memory,including by way of example semiconductor memory devices, e.g., EPROM,EEPROM, and flash memory devices; magnetic disks such as internal harddisks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROMdisks. The processor and the memory can be supplemented by, orincorporated in special purpose logic circuitry.

The invention has been described in terms of particular implementations.Other implementations are possible. For example, the steps of theinvention can be performed in a different order and still achievedesirable results.

The feedback method described can be incorporated in a variety ofpolishing systems. The described method is useful not only for CMPprocess but any polishing process. Adjustment to a polishing process isnot limited to changing the example parameters described. Rather,adjustment can include any combination of the following: changing aslurry rate, changing membrane pressure, changing platen radial speed,changing a combination of membrane pressure and platen radial speed, andchanging the different pressures applied to the back of a substrate.

The eddy current and optical monitoring systems can be used in a varietyof polishing systems. Either the polishing pad, or the carrier head, orboth can move to provide relative motion between the polishing surfaceand the substrate. The polishing pad can be a circular (or some othershape) pad secured to the platen, a tape extending between supply andtake-up rollers, or a continuous belt. The polishing pad can be affixedon a platen, incrementally advanced over a platen between polishingoperations, or driven continuously over the platen during polishing. Thepad can be secured to the platen during polishing, or there could be afluid bearing between the platen and polishing pad during polishing. Thepolishing pad can be a standard (e.g., polyurethane with or withoutfillers) rough pad, a soft pad, or a fixed-abrasive pad. Rather thantuning when the substrate is absent, the drive frequency of theoscillator can be tuned to a resonant frequency with a polished orunpolished substrate present (with or without the carrier head), or tosome other reference.

Although illustrated as positioned in the same hole, the opticalmonitoring system 140 could be positioned at a different location on theplaten than the eddy current monitoring system 40. For example, theoptical monitoring system 140 and eddy current monitoring system 40could be positioned on opposite sides of the platen, so that theyalternately scan the substrate surface.

Various aspects of the invention, such as placement of the coil on aside of the polishing surface opposite the substrate or the measurementof a phase difference, still apply if the eddy current sensor uses asingle coil. In a single coil system, both the oscillator and the sensecapacitor (and other sensor circuitry) are connected to the same coil.

The feedback calculations described can be performed by one or morecomputer program products. These products can interface with thecomputer program products that control the polishing processes. Theproducts for feedback and for control can reside on a same or ondifferent computers. Alternatively, the feedback calculations describedand the polishing process control can be performed by the same computerprogram product.

The substrate described can be any type of substrate. For example, thesubstrate can be a wafer.

The invention has been described in terms of particular embodiments.Other embodiments are within the scope of the following claims. Forexample, the steps of the invention can be performed in a differentorder and still achieve desirable results.

1. A method for generating feedback for chemical mechanical polishing,the method comprising: receiving monitoring information during a secondpolishing process of a first polishing cycle which includes a firstpolishing process and the second polishing process performed on a firstsubstrate that includes a metal layer, the monitoring informationincluding information for two or more sampling regions that correspondto different annular regions of the substrate, the first polishingprocess removing a portion of the metal layer, the second polishingprocess clearing the metal layer from the first substrate during thefirst polishing cycle; calculating, for each sampling region, a clearingtime of the second polishing process, the calculation being based on themonitoring information received; detecting non-uniformity in thecalculated clearing times; generating, from the non-uniformity detected,feedback information for improving the uniformity of a clearing profile;and adjusting the first polishing process in a subsequent polishingcycle of a subsequent substrate, the adjustment being based on thefeedback information.
 2. The method of claim 1, wherein: the firstpolishing process comprises a bulk removal process and the secondpolishing process comprises a slow removal process.
 3. The method ofclaim 1, wherein: the first and subsequent polishing cycles are cyclesof a copper damascene process.
 4. The method of claim 1, wherein themultiple regions of the substrate include annular regions, and whereinmonitoring includes sampling by a system that has two or more samplingregions, each sampling region corresponding to a different annularregion of the substrate, the method further comprising: calculating aclearing time for each sampling region, the calculation being based onthe monitoring information received; calculating an average clearingtime, the calculation being based on the clearing times of the samplingregions; and determining, for each sampling region and for thesubsequent polishing cycle, whether the clearing time calculated for thesampling region needs to be increased or reduced to improve theuniformity of the clearing profile of the second polishing process, thedetermining being based on a ratio of the average clearing time and theclearing time for the sampling region.
 5. The method of claim 1, whereinthe multiple regions of the substrate include annular regions, whereinmonitoring includes sampling by a system that has two or more samplingregions, each sampling region corresponding to a different annularregion of the substrate, and wherein a second polishing process isperformed before the first polishing process during the current and thesubsequent polishing cycles, the method comprising: calculating aclearing time for each sampling region, the calculation being based onthe monitoring information received; calculating an average clearingtime, the calculation being based on the clearing times of the samplingregions; and calculating, for each sampling region and the subsequentpolishing cycle, a target post-polish thickness for the first polishingprocess, the calculating being based on a ratio of the average clearingtime and the clearing time for the sampling region.
 6. The method ofclaim 1, further comprising: receiving traces from one of an opticalmaterial removal monitor, an eddy current material removal monitor, andboth the optical and eddy current material removal monitors.
 7. Themethod of claim 1, further comprising: wherein adjusting the firstpolishing process in the subsequent polishing cycle of the subsequentsubstrate improves uniformity of the clearing times of the secondpolishing process in the subsequent polishing cycle.